This invention relates to fluidized bed combustion and more particularly to a coal injection system for evenly distributing the coal over the cell area.
The need to burn coal as a principal energy source has provided an impetus for examining various methods of burning fuel in an environmentally acceptable manner. Among the methods in which interest has been rekindled is that of burning the coal in a fluidized bed. In a fluidized-bed arrangement, coal and air are reacted in a bed of particulate matter that is agitated by the flow of the air to the extent that it attains a quasi-liquid state. The advantages of this mode of burning coal lie in the ability of the fluidized bed to burn the coal in a comparatively small volume, to conduct heat relatively rapidly to heating surfaces placed in the fluidized bed, and to absorb the sulfur in the coal if the fluidized medium includes material that reacts with the oxidized sulfur.
One type of fluidized bed combustor cell comprises a combustion region with a static bed disposed immediately below the fluidization region. Coal is fed into the static bed and air is blown upward through the bed into the fluidization region in such a manner as to fluidize the coal particles but not the particles making up the static bed.
A typical method of feeding the coal into the bed is through a feed pipe projecting vertically upward into the bed. The coal is distributed throughout the area of the cell by gravity as it overflows from the feed pipe. A major problem associated with such a feed system is that a large number of feed pipes must be used in order to lower the cell area per feed point to ensure that the coal is evenly distributed. Additionally, provision must be made to ensure uniform ignition across the bed which necessarily becomes more difficult as the number of feed points increases.